Waveguides
There is presently an increased interest in integrating in a single semiconductor device both electronic and optical-optoelectronic components. There are several motivations for that: First, the increasing speed demands from micro-electronic processors are being limited nowadays by the capacity of metallic interconnects in a Silicon chip. Optical buses inside the chip would alleviate such limitations. Optical waveguides have significantly larger bandwidth and data-rate capability, and they dissipate less power in form of heat as compared to metallic interconnects. In other applications, the aim of the device is to transmit or receive information to an optical carrier external to the device. In these cases, such a device will contain necessarily an electric-to-optic converting component (i.e. laser or LED) or vice versa optic-to-electric transducer (light detector). That scheme could much benefit from the existence of an efficient waveguide to interface between the transmitter or receiver and an external optical fiber. The two given examples, namely the case of interconnections inside the processor and transmission into an external fiber are in great extent extreme cases regarding the data communication range. There are also intermediate situations in that sense, for example interconnecting between different semiconductor processors or more general devices on a common board or rack. Another consideration in choosing a mean of interconnecting is the manufacturability of the process leading to the fabrication of such a via. Silicon microelectronic and micromachining technologies are highly developed, and the compatibility of the device with such a process is undoubtedly a great advantage. From all these considerations it is clear that it is very desirable to provide a waveguide having the properties of high data throughput, ease of interfacing with an optical fiber, use of low-cost materials, manufacturability and process simplicity. The invention disclosed here has apparently all these mentioned advantages. Another innovative point of the present disclosure is the description of waveguides that are aligned across the supporting wafer, i.e. connect the two opposite sides of the wafer (“vertical waveguides”). This configuration should be useful when one tries to connect both sides of a wafer or sending signals into the back-plane. There are also cases where the transmitter or detector looks in a direction perpendicular to the surface of the wafer.
Several published articles and patents have dealt with the problem of creating waveguides made by combining polymer and other materials on a silicon wafer. Most of previously disclosed material describes a waveguide consisting of a lower cladding layer, a core layer, and an upper cladding layer. U.S. Pat. No. 6,731,856, incorporated by reference in its entirety, describes a method of fabricating such a waveguide on a buffer layer and a core section made of organic polymer which are formed on a substrate. In U.S. Pat. No. 6,671,438, incorporated by reference in its entirety, such a waveguide is fabricated contiguously to etched V-groves to facilitate the position of optical fibers. U.S. Pat. No. 6,356,692, incorporated by reference in its entirety, recognizes the drawback of placing a waveguide on top of the wafer, and alleviates the problem by disclosing a method of thinning the lower clad, and thus reducing the overall height of the waveguide relative to the surface of the wafer. In U.S. Pat. No. 5,526,454, incorporated by reference in its entirety, silicon is used of fabricating a master structure in order to replicate a structure composed by a V-grove for fiber placement attached to a waveguide, the whole component being made out of polymer material.
In all these methods, the waveguide is fabricated on top of the substrate and are not embedded inside the semiconductor material. Regarding the embodiment of the present invention where waveguides are directed substantially perpendicularly to the surface of the wafer. No waveguides of the type described here could we find in the open literature but some previous art can be found regarding the handling of light emitted perpendicularly to the surface of the wafer by Light Emitting Diodes (LED's).
U.S. Pat. No. 5,568,574, incorporated by reference in its entirety, describes a method of transferring a light signal from one surface of the wafer to the opposite one. By the use of a diffraction grating, light is deflected from a horizontal or lateral direction of propagation into a vertical direction (within this document we define “horizontal” direction as parallel to the surface of the wafer or chip and “vertical” direction as normal to the said surface). While propagating through the material in the vertical direction the light will necessarily suffer from diffraction effects as dictated from the laws of optics when light propagates through a homogeneous medium. As a consequence of all these considerations, it is clear that there is need for a technology and method that enables the fabrication of optical waveguides inside the substrate material, both in the horizontal and vertical direction. These waveguides could conduct optical power and information both, beneath the surface of the wafer and across it. These waveguides are distinct from most of the conventional kinds found in literature, where the waveguides are fabricated at the surface itself either above or below them. One exception is the so-called “buried waveguides” fabricated by diffusion in dielectric transparent material by diffusion and further processing (Book-Najafi-: Introduction to Glass Integrated Optics by S. I. Najafi, Artech House Publishers, 1992). This process is not viable in Silicon.
It is noted that U.S. Pat. No. 6,625,366, incorporated by reference in its entirety, of one of the present inventors entitled “Polymer on substrate waveguide structure and corresponding production method” also discloses potentially relevant background material.
Embedded MicroChannels
There is an ongoing need for improved microchannels and improved methods of manufacturing microchannels. The following publications provide relevant background material and are all incorporated herein by reference: “Micromachining of Buried Micro Channels in Silicon” by de Boer et al., Journal of Microelectromechanical Systems, Vol. 9, No. 1, March 200, page 94; U.S. Pat. Nos. 6,462,391; 6,785,134; 6,934,154; 6,903,929; 6,741,469; 6,399,182; 6,602,791; and 5,719,073.